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diff --git a/docs/source/adc.rst b/docs/source/adc.rst index f3d5f55..a749201 100644 --- a/docs/source/adc.rst +++ b/docs/source/adc.rst @@ -20,31 +20,42 @@ number of techniques must be used to get good precision and accuracy. Noise and Bias -------------- -.. FIXME [0.0.11, Maple form factor-specific] - -The biggest issues with analog-digital conversion are noise and bias. -With the Maple, we have tried to isolate the ADC pins and traces from -strong noise sources, but there are always trade--offs between noise, -additional functionality, cost, and package size. - -The 6 ADC pins in a bank (D15--D20) generally have the least -noise, and should be used for fine measurements. If the input voltage -changes relatively slowly, a number of samples can be taken in -succession and averaged together, or the same voltage can even be -sampled by multiple ADC pins at the same time. - -An important factor when taking a voltage reading is the reference -voltages that the sample is being compared against. In the case of the -Maple, the high reference is |vcc| and the low reference is ground. -This means that noise or fluctuations on either |vcc| or ground will -affect the measurement. It also means that the voltage you are trying -to sample must be between ground and 3.3V. +.. FIXME [0.0.12, Maple Native] + +The biggest issues with analog to digital conversion are noise and +bias. With the Maple line, we have tried to isolate the ADC pins and +traces from strong noise sources, but there are always trade-offs +between noise, additional functionality, cost, and package size. +We've tried to enable good analog performance by isolating as many ADC +pins as possible from digital noise on each board. + +More information on these isolated pins is available in each board's +hardware documentation: + +* :ref:`Maple <maple-adc-bank>` +* :ref:`Maple RET6 Edition <maple-ret6-adc-bank>` +* :ref:`Maple Mini <maple-mini-adc-bank>` + +.. :ref:`Maple Native <maple-native-adc-bank>` + +That said, there are a number of more general things you can do to try +to get good readings. If your input voltage changes relatively +slowly, a number of samples can be taken in succession and averaged +together, or the same voltage can even be sampled by multiple ADC pins +at the same time. + +Another important factor when taking a voltage reading is the +reference voltages that the sample is being compared against. In the +case of the Maple, the high reference is |vcc| and the low reference +is ground. This means that noise or fluctuations on either |vcc| or +ground will affect the measurement. It also means that the voltage you +are trying to sample must be between ground and 3.3 V. .. _adc-range: In the case of a variable reading, it is best if the voltage varies -over the entire range of 0--3.3V; otherwise, only a fraction of the -sensitivity is being leveraged. Some basic tools to accomplish this +over the entire range of 0 through 3.3 V; otherwise, only a fraction +of the sensitivity is being used. Some basic tools to accomplish this are `resistor dividers <http://en.wikipedia.org/wiki/Voltage_divider>`_ and `Zener diodes <http://en.wikipedia.org/wiki/Voltage_source#Zener_voltage_source>`_\ |